Forecast Update
Valid: Fri 31 Oct 2008 18:00 to Sat 01 Nov 2008 06:00 UTC
Issued: Fri 31 Oct 2008 18:26
Forecaster: TUSCHY

SYNOPSIS

Please refer to the outlook, issued at Thu 30 Oct 2008 19:20 UTC.

DISCUSSION

... Level-2 area ...

Initiation occured at 16Z SE of Sardinia and since then, rapid thunderstorm development was noticed on HiIR loop. This growing line of storms is just about to enter the Tyrrhenian Sea from the SW. Latest station data over extreme NE Tunisia sample the inflow air very well with surface dewpoints of 22°C and wind gusts near 20m/s during the past 2 hours. Current line of storms is closely linked to compact PVA field, which now leaves NE Algeria, so this line of storms will persist and grow during the next few hours.

Environment is very conducive for storm organisation with current 0-3km shear in excess of 25-30m/s and strong directional shear. Combined with the very moist inflow from the south, tornadoes - some strong - are possible. Damaging wind gust threat spreads northeastwards and there is a significant risk for Lazio, Italy, as GFS still developes winds of 30m/s at 850hPa during the passage of the MCS. Strictly speaking, GFS indicates the possibility of a confined swath with wind gusts in excess of 33m/s, so a level-3 would be warranted. We decided to stick with a 2 as very moist LLJ from the south should provide constant new cell development along the south side of the MCS and hence the more active part with best instability could evolve more to the south (back building), displaced from the most intense winds at 850hPa.

Environment over the N-Adriatic Sea remains very favorable, especially along the coastal areas of the NE/E-Adriatic Sea, as speed and directional shear reach impressive values, so the risk for damaging wind gusts and tornadoes will go on.

Issued a non-thundery level-1 over Slovenia, due to the convective nature of precipitation beside limited instability release, so severe wind gusts could spread well inland.

... Central France ...

New model runs are in, but uncertainties remain. Synop data reveal a return flow over S-France as 10°C-isodrosotherm gradually works its way to the north. We went with the more aggressive runs as current station data over Spain show a somewhat deeper surface depression than forecast. A level-1 was issued for parts of central France due to an isolated tornado and strong to severe wind gust risk also in non-electrified convection. Degree of uncertainty with this forecast remains quite high.